Sometimes brides may confuse a "Day of Wedding Director or Coordinator" to a wedding planner.  It is totally different in many ways both in services and in $!
If you are the bride who wants to have the joy of planning your wedding, making inquiries, looking at magazines, looking at samples, ordering your own invitations, contracting with the vendors you like, then you have most of it done!   The Day of the Wedding is when you want someone to be in "charge" to make sure that YOUR VISION is executed, plus a professional who has experience in dealing with those "last minute" (never failing) issues or complications without the need of  you or your mother's involvement.  Sometimes those things are the ones that you don't want to know about during this time!
A Day of Director will ensure that everything goes as planned.  A Day of Director will orchestrate your rehearsal and instruct everyone their task for the day of, plus tell them where and when to be at certain place... plus answer all questions that ALWAYS come up during the rehearsal!   Then on the Wedding Day, that person will be ensuring that everything goes as planned so that YOU can enjoy all the time possible before the ceremony starts!   The Cost is much less  than a wedding planner.

A Wedding Planner will cost about 8-10% of your total wedding costs. This is for a bride who wants someone else to do everything during the planning stage, set up vendor appointmnts (usually within their preferred vendor list), and take care of everything. 

As anything, the choice of what service and what you want to enjoy during your planning stages is totally up to you!

Good luck and Best Wishes!   AND please enjoy this planning stage! It happens only once in a lifetime!